The present invention relates generally to medical devices and more particularly to a delivery system for a self-expanding implant.
Self-expanding implants are used for numerous medical procedures. For example, a particularly useful type of self-expanding implant is a stent. Stents are commonly used to expand and maintain patency of a vessel suffering from stenosis, and may be used to treat numerous arteries throughout the vasculature. In addition, stents may be used in combination with graft layers to treat aneurysms in the vasculature. Other types of self-expanding implants include filters, valves, etc.
Self-expanding medical implants are typically deployed within a body with a minimally invasive delivery system. Typically, the delivery system has an inner catheter that extends from a proximal handle, which remains outside the patient's body during the deployment procedure, and the distal end of the delivery system, which passes through the patient's body to the treatment site. The self-expanding implant is compressed onto the inner catheter to present a small diameter to ease travel of the delivery system through the patient's body. An outer sheath is positioned over the self-expanding implant and inner catheter to retain the self-expanding implant in the compressed state prior to deployment.
When the delivery system is positioned at the intended treatment site, the physician typically actuates the proximal handle so that the outer sheath is withdrawn from the self-expanding implant and inner catheter. This allows the self-expanding implant to expand outward toward the vessel wall and away from the inner catheter. The inner catheter and outer sheath may then be withdrawn from the patient's body, and the implant may be left at the treatment site.
One problem with conventional delivery systems for self-expanding implants is that it can be difficult to maintain precise control over the implant during the deployment procedure. For example, during deployment self-expanding implants sometimes spontaneously deploy from the delivery system when the outer sheath is only partially withdrawn from the implant. This can occur because the outer sheath is often made from a lubricious material to reduce friction between the self-expanding implant and the outer sheath during withdrawal of the outer sheath. This is an important feature of delivery systems for self-expanding implants because the friction between the implant and the outer sheath can be so high that it can be difficult for the physician to apply enough force to withdraw the outer sheath. However, once the outer sheath has been withdrawn enough to expose the distal end of the implant, the self-expanding implant begins to expand away from the inner catheter. The longitudinal force caused by the distal end of the implant expanding can be enough to pull an additional portion of the implant out of the outer sheath. This can be a particular problem when lubricious materials are used for the outer sheath since the frictional force between the implant and outer sheath is reduced. This can result in imprecise placement of the implant since it can be challenging to predict exactly how the implant will expand during deployment.
In some situations, it may also be desirable to retain a solid connection between the inner catheter and the implant until the outer sheath has been fully withdrawn from the implant. This may be useful if the physician may want to move the implant to a different location after partially deploying the implant. A physician may also want to fully compress a partially deployed implant in order to remove the implant from the patient's body without fully deploying the implant. However, these options are difficult with conventional delivery systems. For example, once a self-expanding implant is partially deployed with a conventional delivery system, the distal end of the implant typically comes into contact with the vessel wall of the patient. When this occurs, friction results between the implant and the vessel wall. If a physician attempts to remove the delivery system in this situation, the friction between the distal end of the implant and the vessel wall will typically pull the remaining portion of the implant out of the outer sheath. In addition, if a physician attempts to push the outer sheath back over a partially deployed implant, the contact between the distal end of the outer sheath and the implant will typically push on the implant and cause the implant to slide distally relative to the inner catheter.
Accordingly, the inventor believes it would be desirable to provide a new delivery system for self-expanding implants with a deployment restraint member.